Dating Old Brass "Nurse's" Buckle

My wife and I picked up this old buckle amongst a box of old brass items at an indoor flea market recently. When I uploaded "Antique Brass Buckle" in Google today, a lot of semi-similar buckles came up and most of the sites called them "Nurse's" buckles which I thought had to do with Nursing mothers since they would have been easy to unbuckle when feeding time came....but no, it was apparently a sales tactic used during Victorian times. Nurses were highly respected and apparently many wore these types of buckles so by calling them nurse's Buckles, they would sell better.
What I would like to know and since there are absolutely no marks is; what style is this buckle and how old would it be?
It measures 3 3/8" wide by 2 1/2" and is Octagonal in shape. Thanks. everyone.